A thick film hybrid integrated circuit is generally composed of elements of conductors and resistors formed on a ceramic substrate by means of screen printing and firing techniques, and semiconductor elements and other electronic parts connected to the conductor or the resistor elements. As the ceramic substrate, alumina ceramics were conventionally mostly used. Recently, silicon carbide ceramics have been developed which have about 10 times as large heat conductivity as the alumina ceramics and a good electrical insulating properties as required for an integrated circuit substrate.
A metallizing paste is used in order to form a thick film hybrid integrated circuit on a ceramic sintered body. The paste is required to form a metallized portion when it is fired, which has good electrical properties, comes into close contact with the ceramic sintered body, and is wettable with solders during the bonding of the semiconductor elements, conductors and other metal connectors.
Conventionally, it is considered that a metallizing paste used for an oxide ceramic sintered body is bonded to the sintered body by a reaction of the molten glass content in the paste with the sintered body. However, the glass melt is disadvantageous in that it causes an incomplete bonding with such a system as silicon carbide sintered body having no reaction between oxides therein, and in that the glass melt hinders the bonding between conductors or other metal connectors and the metallized portion.
A metallizing method and materials for forming elements such as conductors and resistors on a non-oxide ceramic sintered body are disclosed in Japanese Patent Laid-Open Nos. 51774/1980 and 113683/1980. In these specifications, a metallizing method is proposed which includes coating a composition of a metal having a high wettability with regard to the silicon carbide and a metal having a low thermal expansion coefficient and a high melting point such as tungsten and molybdenum to the sintered body in the form of a paste, and firing the coated composition in a non-oxidizing atmosphere. This method, however, is disadvantageous in that a metal having a high melting point such as tungsten and molybdenum is difficult to directly bond with a semiconductor element and requires a material between them which bonds to both the metal and the semiconductor element, when a thick film integrated circuit is formed.